Kerber, who had already advanced from the Red Group, beat Madison Keys 6-3, 6-3 to finish 3-0 in the round robin and eliminate her American opponent. Cibulkova beat Simona Halep 6-3, 7-6 (5) earlier in the day, giving her a 1-2 record.

The top-ranked Kerber will be playing in the semifinals of the season-ending tournament for the first time after failing to advance in three previous attempts. In 2016, the German won the Australian Open and U.S. Open, and reached the final at Wimbledon.

“Today I wasn’t thinking about that I already was in the semis,” Kerber said. “It was important to go out to win the match and win all three matches.

“Now I’m going to the semis with three really good matches which gives me a lot of confidence.”

In the match with Keys, half of the 18 games resulted in service breaks. Kerber broke Keys’ serve on six of seven offerings, while Keys took advantage of three of four break points.

“I think today I, again, played with nerves,” Keys said. “I have to learn to separate my feelings and emotions when I’m in high-stress situation. It’s something I need to work on.”

Keys and Halep, who had her left knee taped for the early match, also finished the group with 1-2 records, but finished behind Cibulkova in the standings.